Electrical fly-by-wire system for operating an aircraft rudder

ABSTRACT

Electrical fly-by-wire system for operating an aircraft rudder.  
     According to the invention:  
     said system comprises, between the rudder bar ( 7 ) and the actuator ( 9 ) of the rudder  1 , filtering means ( 12 ) of the-low pass type receiving the control command (y) and generating an operating command (yf) for said actuator ( 9 ); and  
     the higher the fraction of the maximum value of travel of said rudder ( 1 ) to which the amplitude of said control command (y) corresponds, the higher the time constant of said filtering means ( 12 ).

[0001] The present invention relates to an electrical fly-by-wire system for operating an aircraft rudder.

[0002] It is known that, at the present time, in most aircraft, a rudder is operated via a mechanical link positioned between the rudder bar actuated by the pilot and said rudder. However, electrical fly-by-wire operation of such a rudder has already been envisaged, in the image of what is already done with the other control surfaces, the flaps, ailerons, spoilers, etc.

[0003] Furthermore, it is known that such a rudder is engineered on the basis of calculated loadings applied to said aircraft during standardized maneuvers. In roll and yaw, these maneuvers consist in influencing the rudder by sharp actions on the rudder bar, up to the point where said rudder has reached its full travel.

[0004] A subject of the present invention is an electrical fly-by-wire system for operating a rudder, by virtue of which it is possible to limit the lateral loadings applied during maneuvers to said rudder and therefore reduce the size and mass thereof, without thereby reducing the flyability of the aircraft or flight safety.

[0005] To this end, according to the invention, the electrical fly-by-wire system for operating an aircraft rudder, said rudder being mounted so that it can rotate about an axis so that it can adopt any angular position whatsoever within a range of travel extending on each side of the neutral position of the rudder and limited on each side of this neutral position by a maximum travel value, and said system comprising:

[0006] a rudder bar actuated by the pilot and associated with a transducer that delivers an electrical control command that represents the action of the pilot on said rudder bar; and

[0007] an actuator receiving an operating command derived from said control command and moving said rudder about said axis,

[0008] is notable:

[0009] in that, between said rudder bar and said actuator there are filtering means of the low-pass type receiving said control command from said transducer and generating said operating command for said actuator; and

[0010] in that the higher the fraction of said maximum travel value to which the amplitude of said control command corresponds, the higher the time constant of said filtering means.

[0011] Thus, by virtue of the present invention, non-linear filtering which depends on the travel available to the rudder is introduced into the control commands at the rudder bar, this filtering being all the greater the nearer said rudder gets to the end stops delimiting maximum travel, thus limiting the loadings applied to said rudder and therefore making it possible for its size and mass to be reduced.

[0012] Furthermore, it is known that it is customary for an operating system of the type recalled hereinabove to comprise, in addition, yaw-stabilizing means that generate a stabilizing command which is added to the control command at the rudder bar. In this case, the level of the maximum loadings on said rudder becomes particularly critical when these commands are of the same sign.

[0013] Hence, according to another particular feature of the present invention, when said operating system additionally comprises means for stabilizing said aircraft in terms of yaw generating a yaw-stabilizing command and a first adder summing said yaw-stabilizing command and said actuator operating command, means are provided which are capable of determining whether said control command and said yaw-stabilizing command are of the same sign or of opposite signs, and said determining means act on said filtering means to increase their time constant when said control command and said stabilizing command are of the same sign.

[0014] Thus, the loadings applied to the rudder are reduced even more by further filtering of the control command at the rudder bar when said rudder is close to its position of maximum travel and when this command and the yaw-stabilizing command are of the same sign.

[0015] In a practical embodiment, the system according to the present invention comprises:

[0016] a limiter receiving said control command and delivering an output signal which is:

[0017] either said control command, when the amplitude thereof corresponds to a travel value below a limit equal to a predetermined fraction of said maximum travel value;

[0018] or a limit value corresponding to said limit when the amplitude of said control command is greater than this limit value;

[0019] a first low-pass filter having a first time constant and receiving said output signal from said limiter;

[0020] a subtractor calculating the difference between said control command and said output signal from said limiter;

[0021] a second low-pass filter having a second time constant higher than said first time constant and receiving said difference calculated by said subtractor; and

[0022] a second adder summing the output signals from said first and second filters, so as to generate a filtered control command for said actuator.

[0023] When this system is provided with the aforementioned yaw-stabilizing means, it may additionally comprise:

[0024] a third low-pass filter having a third time constant higher than said second time constant and receiving said difference calculated by said subtractor;

[0025] a controlled switch inserted between said second and third low-pass filters, on the one hand, and said second adder, on the other hand, so as to be able to send to said second adder, either the output signal from said second low-pass filter or the output signal from said third low-pass filter; and

[0026] means of controlling said switch in such a way that the latter:

[0027] connects said second low-pass filter to said second adder when said yaw-stabilizing command and said electrical control command are of opposite signs; or

[0028] connects said third low-pass filter to said second adder when said yaw-stabilizing command and said electrical control command are of the same sign.

[0029] As a preference, said first, second and third low-pass filters are of the first-order type, with a transfer function in the form $\frac{1}{1 + {\tau \quad p}},$

[0030] , τ being the respective time constant τ1, τ2 or τ3 of the first, second and third filters and p being the LAPLACE variable.

[0031] The first (τ1), second (τ2) and third (τ3) time constants may have respective values of between 100 ms and 500 ms; 500 ms and 1 second; and 1 second and 2 seconds.

[0032] Furthermore, said limit may correspond to roughly 70% of said maximum value of travel of said rudder.

[0033] The figures of the appended drawing will make it easy to understand how the invention may be embodied. In these figures, identical references denote elements which are similar.

[0034]FIG. 1 shows the block diagram of one embodiment of the electrical fly-by-wire operating system according to the present invention.

[0035]FIG. 2 is a diagram illustrating, in a plan view, the movements of the aircraft rudder operated by the system of FIG. 1.

[0036]FIGS. 3, 4 and 5 illustrate the filtering of the operating commands for the rudder, for three different command amplitudes, respectively.

[0037] The electrical fly-by-wire operating system according to the present invention and depicted in FIG. 1 is intended to operate an aircraft rudder 1 mounted to rotate in both directions about an axis Z-Z in the way symbolized by the double headed arrow 2. As illustrated in the schematic plan view of FIG. 2, the rudder 1 can adopt any angular position whatsoever about said axis Z-Z within a range of travel 3 extending on each side of the aerodynamically neutral position 4 of said rudder 1. The range of travel 3 is limited on each side of the neutral position 4 by a position 5D or 5G, corresponding to the maximum travel value M (to the right and to the left respectively) and embodied by end stops 6 for the rudder 1.

[0038] The electrical fly-by-wire operating system comprises a rudder bar 7 available to the pilot (not depicted), associated with a transducer 8 delivering an electrical yaw-control command y, and an actuator 9 receiving, from the output of an adder 10, an operating command c capable of moving said rudder 1 about the axis Z-Z.

[0039] The electrical fly-by-wire operating system of FIG. 1 additionally comprises yaw-stabilizing means 11 (flight computer) generating a yaw-stabilizing command s sent to one of the inputs of the adder 10. The other input of said adder 10 receives a command yf, corresponding to said yaw-control command y after filtering via an arrangement 12 arranged between the transducer 8 and the adder 10.

[0040] The operating command c for the actuator 9 is therefore the sum of the filtered command yf and of the yaw-stabilizing command s.

[0041] The filtering arrangement 12 comprises a limiter 13 receiving, at its input 13E, said yaw-control command y and capable of limiting it in amplitude to a limit value l corresponding to a predetermined fraction L of the maximum travel value M. For example, the limit L is equal to 70% of the maximum value M (see FIG. 2). The limiter 13 operates as follows:

[0042] if the amplitude y1 of the control command y is less than the limit value l, it is said signal y which appears at the output 13S of the limiter 13;

[0043] by contrast, if the amplitude y2 of the control command y is greater than the limit value l, it is this limit value l which is present at said output 13S.

[0044] Said filtering arrangement 12 additionally comprises three first-order low-pass filters 14, 15 and 16, a subtractor 17, an adder 18, a controlled switch 19, an operating device 20 for said switch, and a multiplier 21.

[0045] These various elements are connected as follows:

[0046] the input 14E and the output 14S of the filter 14 are connected respectively to the output 13S of the limiter 13 and to one of the inputs 18E1 of the adder 18;

[0047] the positive input 17P and the negative input 17N of the substractor 17 are connected respectively to the output of the transducer 8 and to the output 13S of the limiter 13, so that said subtractor 17 at its output 17S delivers the difference between the electrical yaw-control command y and this same command limited by the limiter 13;

[0048] the inputs 15E and 16E of the filters 15 and 16 are connected in common to the output 17S of the subtractor 17;

[0049] the outputs 15S and 16S of the filters 15 and 16 are connected respectively to the two inputs 19E1 and 19E2 of the controlled switch 19;

[0050] the output 19S of the controlled switch 19 is connected to the other input 18E2 of the adder 18, so that the latter receives either the signal filtered by the filter 15 or the signal filtered by the filter 16, depending on the position of the switch 19;

[0051] the control device 20 operating the switch 19 is itself controlled by the multiplier 21 which receives both the yaw-stabilizing command s and the yaw-control command y.

[0052] The way in which the system according to the invention works is described hereinafter with reference to the diagrams of FIGS. 3, 4 and 5, which represent the yaw-control command y as a function of time t, said diagrams also carrying the limit values l and m corresponding respectively to the limit angular values L and M.

[0053]FIG. 3 depicts the scenario in which the given command y is in the form of a square pulse 22, the amplitude y1 of which is below the limit l. In this case, the limiter 13 allows the square pulse 22 to pass in its entirety, and this appears at its output 13S. Thereafter:

[0054] the subtractor 17 receives the same square pulse 22 on its two inputs 17P and 17N, which means that no signal is present on its output 17S and neither of the filters 15 and 16 is active;

[0055] the filter 14 receives the square pulse 22 and filters it, rounding off the sharp rising 22A and falling 22R edges, in the way depicted in FIG. 3.

[0056] The signal yf in this case therefore consists entirely of this square pulse with rounded rising and falling edges 22A and 22R.

[0057] If, now, the given command y is in the form of a square pulse 23, the amplitude y2 of which is above the limit value l (see FIGS. 4 and 5), the limiter 13 is active and at its output 13S delivers a square pulse corresponding to the square pulse 23, but limited to the amplitude l. Thereafter:

[0058] the filter 14 receives the square pulse 23, capped of its excess 24 above the amplitude; and

[0059] the subtractor 17 delivers on its output 17S said excess 24 above the amplitude l, sent to the inputs 15E and 16E of the filters 15 and 16.

[0060] The square pulse 23, capped of the excess 24 is filtered by the filter 14 in the way similar to the one indicated above for the square pulse 22 (note the rising and falling edges 23A and 23R).

[0061] In addition, said excess 24 is filtered either by the filter 15 or by the filter 16, depending on the signs of the commands y and s.

[0062] If these signs are opposite, something which is detected by the multiplier 21, the switch 19, controlled by the device 20, connects the output 15S of the filter 15 to the input 18E2 of the adder 18, so that this excess 24 is filtered by the filter 15, more strongly than the filter 14 filters the capped square pulse 23, as indicated by the curved segment 25 in FIG. 4. This figure also represents, in dashed line, by way of comparison, the continuation of the rounded rising edge 23A that would have resulted from filtering by the filter 14.

[0063] By contrast, if the commands y and s are of the same sign, the device 20, under the control of the multiplier 21, switches the switch 19 so that the output 16S of the filter 16 is now connected to the input 18E2 of the adder 18. The excess 24 is therefore more strongly filtered by the filter 16 than by the filter 15, as shown by the curved segment 26 in FIG. 5. In this last figure, dashed line has been used, for comparison purposes, to depict the continuations of the rounded rising edge 23A which would have resulted from filtering by the filters 14 and 15 respectively.

[0064] In both instances of FIGS. 4 and 5, the filtered command yf therefore consists of the sum of the capped square pulse 23, filtered by the filter 14, and of the excess 24, filtered either by the filter 15 or by the filter 16 (FIG. 4 or FIG. 5).

[0065] The low-pass filters 14, 15 and 16 have time constants which, for example, are respectively between 100 ms and 500 ms; 500 ms and 1 second; and 1 second and 2 seconds. Thus:

[0066] the filtering afforded by the filter 14 corresponds to high flyability criteria;

[0067] the filter 15 allows a significant reduction in the loadings applied to the rudder, when the action on the rudder bar and the action of the yaw stabilizer oppose one another; and

[0068] the filter 16 allows a significant reduction in said loadings even when the action of the rudder bar and the action of the yaw stabilizer combine.

[0069] Such a reduction in the loadings applied to the rudder allows its size and therefore mass to be reduced. 

1. An electrical fly-by-wire system for operating an aircraft rudder, said rudder being mounted so that it can rotate about an axis so that it can adopt any angular position whatsoever within a range of travel extending on each side of the neutral position of the rudder and limited on each side of this neutral position by a maximum travel value, and said system comprising: a rudder bar actuated by the pilot and associated with a transducer that delivers an electrical control command that represents the action of the pilot on said rudder bar; and an actuator receiving an operating command derived from said control command and moving said rudder about said axis, and in which system: between said rudder bar and said actuator there are filtering means of the low-pass type receiving said control command from said transducer and generating said operating command for said actuator; and the higher the fraction of said maximum travel value to which the amplitude of said control command corresponds, the higher the time constant of said filtering means.
 2. The system as claimed in claim 1, additionally comprising means for stabilizing said aircraft in terms of yaw generating a yaw-stabilizing command and a first adder summing said yaw-stabilizing command and said actuator operating command, and in which system: there are also means capable of determining whether said control command and said yaw-stabilizing command are of the same sign or of opposite signs; and said determining means act on said filtering means to increase their time constant when said control command and said stabilizing command are of the same sign.
 3. The operating system as claimed in claim 1, which system comprises: a limiter receiving said control command and delivering an output signal which is: either said control command, when the amplitude thereof corresponds to a travel value below a limit equal to a predetermined fraction of said maximum travel value; or a limit value corresponding to said limit when the amplitude of said control command is greater than this limit value; a first low-pass filter having a first time constant and receiving said output signal from said limiter; a subtractor calculating the difference between said control command and said output signal from said limiter; a second low-pass filter having a second time constant higher than said first time constant and receiving said difference calculated by said subtractor; and a second adder summing the output signals from said first and second filters, so as to generate a filtered control command for said actuator.
 4. The system as claimed in claim 3, wherein said first low-pass filter is of the first-order type.
 5. The system as claimed in claim 3, wherein said first time constant of said first low-pass filter is between 100 ms and 500 ms.
 6. The system as claimed in claim 3, wherein said second low-pass filter is of first-order type.
 7. The system as claimed in claim 3, wherein said second time constant of said second low-pass filter is between 500 ms and 1 second.
 8. The system as claimed in claim 3, wherein said limit is equal to approximately 70% of said maximum travel value.
 9. The system as claimed in claim 3, which system additionally comprises: a third low-pass filter having a third time constant higher than said second time constant and receiving said difference calculated by said subtractor; a controlled switch inserted between said second and third low-pass filters, on the one hand, and said second adder, on the other hand, so as to be able to send to said second adder, either the output signal from said second low-pass filter or the output signal from said third low-pass filter; and means of controlling said switch in such a way that the latter: connects said second low-pass filter to said second adder when said yaw-stabilizing command and said electrical control command are of opposite signs; or connects said third low-pass filter to said second adder when said yaw-stabilizing command and said electrical control command are of the same sign.
 10. The system as claimed in claim 9, wherein said third low-pass filter is of the first-order type.
 11. The system as claimed in claim 9, wherein said third time constant of said third low-pass filter is between 1 second and 2 seconds. 